The present invention relates generally to spark arrestors for small internal combustion engines, and more particularly, to a spark arrestor that is mounted external to the muffler.
Spark arrestors for preventing sparks from being discharged with exhaust gases from an internal combustion engine are well known in the art. Generally, spark arrestors are screen assemblies which filter the carbon from the combustion gases, thereby preventing the possible ignition of the carbon as the gases are exhausted from the muffler, which may result in a fire hazard. Spark arrestors may be internal, i.e., incorporated into the design of a muffler for an internal combustion engine, or external, i.e., mounted directly to an exhaust discharge pipe or to the discharge side of a muffler.
Internal spark arrestors add additional parts to a muffler assembly and may be difficult to clean if the muffler cannot be easily disassembled. Moreover, an internal spark arrestor incorporated into a muffler which cannot be disassembled may restrict the flow of exhaust gas, e.g,. from carbon build-up on the spark arrestor, and thereby cause excessive back pressure within the internal combustion engine. Thus, internal spark arrestors may cause inadequate engine performance after a period of use.
U.S. Pat. No. 3,677,364, issued to Pawlina illustrates an internal spark arrestor which may be used with an internal combustion engine. In the Pawlina patent, a spark arrestor is mounted within a muffler at the discharge end of the muffler, and an end cap having a plurality of exhaust holes is provided to protect the spark arrestor from physical damage. Such a spark arrestor may effectively arrest the discharge of sparks from an internal combustion engine. Notwithstanding this successful performance, efforts are continuously directed toward providing a more cost-efficient spark arrestor.
External spark arrestors of conventional design use a plurality of fasteners, e.g., screws or bolts, for attachment. The spark arresting screen is rigidly attached, usually by welding, to a metal ring adapted to be fastened to the muffler by a plurality of fasteners. The demand for such spark arrestors is not sufficient to allow automation of the associated manufacturing processes, and the cost of such spark arrestors tends to be relatively expensive because of the labor intensive construction process.
U.S. Pat. No. 1,532,473, issued to Byrne illustrates an externally mounted spark arrestor. The spark arrestor of Byrne is mounted directly to the end of an exhaust conduit of an internal combustion engine. The exhaust conduit is provided at the discharge end with an outwardly extending flange having two threaded mounting holes. A second flange is provided for receiving and allowing attachment of the spark arrestor screen to the flange of the exhaust conduit by two threaded bolts. Thus, the Byrne patent requires a plurality of fasteners to connect the spark arrestor to the exhaust conduit.